The present invention relates to apparatus for admixing plural fluids, and more particularly, the present invention relates to apparatus for admixing a foam solution with water in a predetermined proportion in a foam-water fire fighting system.
The present invention is described in Disclosure Document No. 018,855 filed May 2, 1973.
In foam-water fire fighting systems, the demand for the foam-water mixture can be expected to vary considerably, depending upon the rate of application of the mixture. For instance, it is not uncommon for the flow rate to vary from as low as 50 gpm to as high as 1,000 gpm during fire fighting operations. In order to ensure satisfactory results, the foam should be mixed with water in a predetermined proportion, and the proportion should be relatively constant over this entire flow range. Usually when an AFFF foam is employed, the foam is mixed with water in a ratio of 6/94 in suitable mixing apparatus connected in the supply line. In order to maintain adequate pressure at the nozzle to ensure proper distribution of the mixture, the apparatus which admixes the foam with the water should create a minimum of pressure drop in the supply line.
An example of apparatus which is used to admix a foam solution with water in a foam-water fire fighting system is disclosed in U.S. Pat. No. 3,647,002. Although the patented apparatus may function satisfactorily, it has a number of moving parts, and hence it is relatively complex. Because of the complexity, the patented apparatus may not be as reliable as a simpler structure would be. In addition, the patented valve structure is spring-loaded into a closed position. Hence, the water must act against increasing spring pressure as the water flow rate through the valve increases, and this has the effect of increasing the pressure drop across the valve at higher flow rates and reducing pressure at the discharge nozzle. As a result, the effectiveness of distribution of the mixture may be significantly impaired.
With the foregoing in mind, it is a primary object of the present invention to provide novel apparatus for admixing a primary fluid with a secondary fluid in a relatively constant proportion over a wide range of flow rates of the mixed fluids.
It is another object of the present invention to provide improved apparatus for admixing a foam solution with water in a foam-water fire fighting system in manner which accurately meters the amount of foam mixed with the water to ensure an optimum proportion of foam to water over a wide range of flow rates of the foam-water mixture.
It is a still further object of the present invention to provide plural fluid proportioning apparatus which operates with a minimum of pressure drop through the apparatus over a wide range of flow rates through the apparatus.
As a further object, the present invention provides unique foam-water mixing apparatus which is relatively simple in construction so as to be highly reliable and relatively trouble-free in operation.
A further object of the present invention is to provide a simple plural fluid proportioning valve wherein the mixing proportion may be changed relatively easily.
It is still another object of the present invention to provide a novel balanced-pressure valve. As yet another object, the present invention provides a unique valve which is biased by gravity into a closed position.
More specifically, in the present invention, apparatus is provided for admixing a primary fluid with a secondary in a predetermined proportion over a wide range of flow rates of the fluid mixture. To this end, the apparatus comprises a body having an inlet cavity, an outlet chamber which overlies the inlet cavity, and a free-floating disk-like valving member mounted in the outlet chamber. An annular port is provided between the cavity and the chamber, and a reservoir having an orifice opening upwardly into the chamber is provided in the cavity interiorily of the annular port. The secondary fluid is supplied to the reservoir at a relatively constant pressure corresponding to the pressure of the primary fluid at the inlet cavity. The valving member extends across the annular port and has a tapered plug which depends into the orifice, and the valving member carries a mass of a predetermined weight which biases the member into a position blocking fluid flow through the annular port. A primary fluid flows upwardly through the annular port and laterally out of the chamber, and as the primary fluid flows, it elevates the valving member into a position corresponding to its rate of flow. As the valving member moves vertically in response to changes in the primary fluid flow rate, the area between the plug and the reservoir orifice also varies to ensure mixing of a precise amount of secondary fluid with primary fluid in the mixing chamber. With this structure, the pressure drop across the apparatus remains relatively constant over a wide range of flow rates.
The present invention also provides a balanced pressure valve which is particularly useful in combination with the above proportioning valve to supply the secondary fluid to the reservoir at a pressure corresponding to the supply pressure of the primary fluid. The valve is designed to bypass secondary fluid to its supply tank in response to changes in pressure of the primary fluid at the inlet to the apparatus as determined by a pressure-responsive diaphragm connected to a valve operator. The valve has a spool and neck which are slidable axially relative to spaced outlets in response to movement of the diaphragm. The spool, neck and operator are diminsioned relative to one another to prevention pressure forces from adversely affecting movement thereof.